Phonograph sound box



FHONOGRAPH SOUND BOX 1 I l i March 3, 1931. J. wEfNBERGER 1,795,154

PHONOGRAPH SOUND BOX Filed Sept. 50, 1925 2 Sheets-Sheet 2 INVENTOR JULIUS EINBERGER /zq ra/mao ATTORNEY Talented Mar., 3, 1931 NlTED STATES PATENT OFFICE JULTUS WTEINABERGER, OF NEW YORK, N. Y., ASSIGNOR, T RADIG CORPORATION' 01?' AMERICA, A COR'PURATION 0F DELAWARE PHONOGRAPH SOUND BOX Application filed September 30, 1925. Serial No. 59,516.

The invention concerns sound reproducing devices 'and has for its principal object to provide such a device with Igreatly improved operating characteristics.

Another object of the invention is to provide such a device comprising ai vibratory element having a natural period of vibration outside of the normal operating frequency range of the device.

A further object of the invention is to provide such a device in which the vibratory element is highly damped.

Still another object of the invention is to provide such a device having a diaphragm with a natural period of vibration outside the normal operating frequency range of the device and provided with a plate placed close to the diaphragm to provide a small air space between it and the diaphragm.

Still another object of the invention is to provide such a device having a' stretched metallic vibratory member separated from a plate by a small air space.

While not limited to such a use the invention has particular application to phonograph sound boxes and it will be explained in connection with these devices to clearly bring out its salient features.

It is customary at present Ito construct sound boxes having a diaphragm of mica or reproduction. First, the diaphragms mentioned all have natural frequencies of vibration which lie within the ordinarymusical range. Usually this natural diaphragm frequency is of the order of a few hundred to 1000 cycles. `Also, the cavity formed by the diaphragm and back plate, due to the relatively large spacing employed, has a fundamental natural frequency of the order of magnitude of a few hundred cycles. The natural frequencies of the diaphragm and cavity cause them to resonate to certain tones in the range mentioned, and thus give unduly large response to these frequencies; on the other hand, frequencies considerably removed from this range, such as low frequencies of the order of fty cycles or high frequencies in excess of say two thousand cycles are poorly reproduced.

In order to secure accurate reproduction of music or speech, it is necessary toI reproduce with substantially the same volume frequencies ranging from about 30 to Well above 5000 cycles. In fact, to reproduce the letter s it is necessary to obtaingood volume up to about 10,000 cycles. The low frequencies in music, of the order of 30 to 200 cycles, appear, for example, in the low notes of the piano, the bass viol, the kettle drums, the bass and baritone voices. The high frequencies are similar material. For example, cardboard, necessary to obtain true reproduction of the paper, animal skins or membranes have been used as diaphragms. Such materials are loosely held at the edge in soft rubber gas- 35 kets or clamped tightly. One side of the diaphragm is left open, and the lever arm to which the reproducing needle is attached is connected at this side. The other si'defaces the rear of the sound box, which is usually 40 situated at a distance of a tenth of an inch vfrom the diaphragm, and in the center of this back plate is a large hole perhaps half an` inch in diameter which leads to the horn.

Sound boxes of this type have several char- 45 acteristics which are detrimental to accurate quality of instruments or voices; that is, voices singing a tone of, say, 500 cycles, may have harmonics up to 5000 or 10000 cycles which cause it to possess its particular quality. On the other hand, the resonance of the usual types of phonograph sound boxes may give an entirely false quality to a voice or instrument; for example, if a baritone is singing a fundamental tone of 250 cycles and the sound box reproduces 750 cycles much more loudly than 250, the third harmonic (750 cycles) of th'e voice will be reproduced out of all proportion to its true relative value with respect to the fundamental of 250 cycles and the tone as reproduced will sound more like a tenor voice the fundamental tones employed in the singing voice range, and the cavity between the diaphragm and the back ofthe sound box is -v made small in volume so as to also have a very high natural frequency. T'he order of magnitude of the diaphragm frequency is from 5000 to 15000. cycles, although it will be clear that the specification of these definite fre-A quency limits does not implyf that the invention is limited to this range; they are merely cited to give some idea of the order of the fre! quency which is regarded as suitable. The spacing between diaphragm and back of the sound box may be made of the order of a few hundredths or even a few thousandths of an inch. A further object accomplished by thisreduced spacing is that the small volume of enclosed air helps to damp the vibration. of

' the diaphragm and smooths outits frequencyres'ponse characteristic.

The high natural frequency in the diaphragm may be secured by constructing it out of a thin. metallic material, and then stretching it. The material used may be steel br strong aluminum alloy (such as duralumin) ,l or molybenum; in fact, any metal that will withstand the stretching strain is suit? able. The thiclrless of material employed is a few thousandths of an inch, the diameter of the diaphragm being of the order of one to three inches. Such a diaphragm when unstretched, will have a natural frequency of: a few hundred cycles, similar to the ordinary non-metallic phonograph diaphragm. .-'But by subjecting it to the stretching process, its natural frequency lmay be' raised as high as desired, within the limits of strength l-of the material. It is easily possible to secure a natural frequency of A6000 cycles with any of 3 the materials mentioned, and one may go as highas 15000 cycles with steel diaphragms.

4It'."willhe seen, therefore, that the sound box-of@thisf'invention differs from those in A.ordina'ry'tuse in that it employs a diaphragm j of metal, stretched so as to have a high natu- AB0.

ral frequency, as 'opposed to the ordinary unstretched, non-metallic, low frequencydia-- phragms.

The invention is illustrated by way of example in .the accompanying drawings in which,

Fig. 1 shows a group of comparative curves comparing the operation of the device with a'previous device of similar nature,

Fig.' 2 is a sectional view of a phonograph sound box illustrating the invention and Fig. 3 is a sectional view of a modication of the device shown in Fig. 2.

Referring now to Fig. 2, the diaphragm indicated by 1 is firmly clamped between two heavy metal rings 2, 2, by means of ridges or threads as shown at 3, 3. The diaphragm is stretched by bringing the blunt edge of ring( 4. up against'one side by means of the ring 5 revolving in a thread in 2, and the ring 6 up against the other side by means of screws 7. The pressure exerted by means of rings 4 and 6 is controlled in such fashion that the diaphragm is kept in a vertical plane but at the same time is gradually stretched until it has some particular desired natural fre-f phragm and the back plate 8 and the latter is held in position ,by means of the clamping member 10, which-is adjustably clamped against the plate 8 by means of the screws 18. The thickness of the washer thus determines the -spacingbetween diaphragm and back plate. series of holes indicated at l1, near the outer edge of the diaphragm, so that the sound may pass from the cavity between diaphragmI and back plate into the horn. The dimensions of these holes may be advantageously chosen to diminish the easevof passage of sounds having frequencies of the order of the natural frequency of the diaphragm, and thus diminish scratch (the latter being in large part due to shock-excitation of the diaphragm into its natural modes of vibration by the friction of the needle on the record.) The horn or tone arm 12 may be connected to the sound box in any convenient manner. The needle holder 13 and lever arm 14 are attached to the front of the diaphragm by wax, as at 15, or in any other convenient manner.

The difference in frequency response y characteristics of the high natural frequency stretched diaphragm and anl unstretched diaphragm of the conventional type is illustrated in Fig. 1. v It will be seen that the conventional type gives a widely varying response in the important range from() to 4000" cycles,

-while the stretched diaphragm'is practically uniform in response. The response of the latter does increase at its resonant frequency, but this -is considerably outside the range of The latter is providedl with al the musical tones ordinarily employed andhence is of no practical consequence.

Obviously the action of the damping plate represented by 8 in Fig. 2 is not dependent on its position in the rear of the dia hragm and it may, if desired, be placed in ront of the diaphragm. This construction is shown in Fig. 3 in which the same reference numerals with the primes added designate parts corresponding to those in Fig. 2. ln this modication an aperture is provided in the plate 8 to permit the angular extension of the arm 14 to pass through. The plate 8' is held in position by the riglO fastened to one of the rings 2 by suitable screws. The ring 10 is adjustably clamped against the plate 8 by means of the screws 18. This.

construction leaves theside of the diaphragm facing the horn opening free, which may be advantageous in certaln cases. If 4desired the plate 8 may beV made in two pieces so that the lever arm 14 ma be attached t'o the diaphragm at 15 convenlentl. and the plate 8 then placed against the iaphragm and secured by clamp 10.

It is obvious that the construction indicated may be adapted for use on records made in hill and dale as Well as side-cut form or in any other manner. Also7 the same principles may be applied to sound boxes arranged to convert the motion of the needle to relectric currents, as for example, such wherein the diaphragm is utilized as an element of a condenser transmitter or as an electromagnetic element to induce currents in a magnet winding; and such applications are regarded as within the scope ofthe invention.

It is also obvious that mechanical arrangements can be devised of dierent form than those shown in the drawings which will accomplish the same results and such arrangements are'also regarded as-within the scope ofs the invention. Also a mica diaphragm may be substituted for the metal one in certain cases.

Having now described my invention, I claim 1. A device for translating mechanical vibrations into sound comprising a 4diaphragm, means for increasing the natural frequency of said diaphragm above the normal operating frequency range of said device and a rigidY non-vibratory plate in proximity to one face of the diaphragm and spaced therefrom to form a cavity having a natural resonant period above the normal operating frequency range of said device.

2. A phonograph sound box comprising a. diaphragm and a rigid non-vibratory plate in proximity to one of the faces thereof andso located as to form a cavity having a natural resonant frequency above the normal operating frequency range of said sound box.

3. A phonograph sound box cemprising a plate.

J ULIUS WEINBERGER. 

